Gamma imaging Flashcards
what is a stable nuclei?
Here they would contain equal number of protons and neutrons.
P = N
what is alpha particle?
This is helium where there is a very stable combination of 2 protons and 2 neutrons.
The heavier nuclei contain a greater proportion of ……..
neutrons.
define isotopes:
These are nuclides that have the SAME no of protons (atomic no), position in the periodic table, and chemical and metabolic properties but different number of neutrons, mass no and density and other physical properties.
Name the isotopes of carbon
All carbon atoms contain 6 protons.
99% of stable nuclei are C12- 6 N
1% are C13- 7N
C11- 5 N- neutron defficient
C14- 8N- Neutron excess- the last two are unstable and radioactive.
Name naturally occuring radionuclides;
uranium radium radon C14 and K40 these contribute to our background radiation exposure
what process happens in a nuclear reactor?
Give example;
when an additional neutron is forced into a stable nucleus –> Neutron excess
Mo98 + N = Mo99
what happens to atomic no and mass no in neutron excess
the atomic number is unchnaged, but the mass number has increased by 1
Z = p = e A = p +n
T/F?
the radionuclides produced in a nuclear reactor can be separated from the original stable nuclides.
False
the radionuclides produced in a nuclear reactor can NOT be separated from the original stable nuclides.
This is because they have the same atomic no and hence same chemical properties.
They CANNOT be made carrier free.
T/F?
Radionuclides produced in a reactor can be made carrier free.
False
Radionuclides produced in a reactor CANNOT be made carrier free.
because they have the same atomic no and hence same chemical properties. they cannot be made separate.
what happens in neutron deficient nuclide?
A proton is forced into a stable nuclide forcing out a neutron.- neutron deficient unstable nuclide.
what process happens in a cyclotron?
give example;
neutron deficient nuclide are produced in a cyclotron-
Force a p, knock out a n = neutron deficient
O18 + p = F18 + n
what happens to atomic no and mass no in neutron deficient cyclotron?
[A = p+n, Z=p=e]
Mass number is the same.
The atomic number has increased by 1
radionuclides produced in a cyclotron can be obtained carrier free. Why?
Because the have different atomic no and hence different chemical properties
They are also short lived. so they should be used relatively close to the cyclotron
please read the statement.
radioactive fission products may be extracted from the spent fuel rods of nuclear reactor
U238 = Mo99 + other fission by product.
why would Mo be separated and prepared in a very pure form?
because its different chemically from the other products.
what is produced in a generator?
daughter products are obtained from generators.
they contain longer lived radioactive parent.
Tc99m from Mo99 generator - Mo/Tc
positron emitter gallium 68 from germanium generator. Ge/Ga generator
what happens in B- decay?
The radionuclide with n excess may lose energy and become stable by a n –> p + e.
The e is then ejected with high energy and is referred to as a -ve beta particle.
what happens to atomic and mass no in beta- decay?
A = p+n Z = p= e
Mass number is the same
The atomic number +1
what happens to excess energy in beta- decay?
usually it loses this immediately with the emission of one or more gamma photons.- leaving daughter nuclei with minimum energy in the ground state.
list the isomeric transition for Mo99
Mo99………B-, gamma, 67h…..>Tc99m…..gamma,6h….> Tc99………..B-, gamma……> stable 99Ru (Ruthenium)
what is the difference between Tc99 and Tc99m?
they are isomers, they have different energy state and half lives but otherwise indistinguishable as regards to mass number, atomic no, and other properties.
what sort of radiation Mo99and Tc99m emit?
Mo99 = emits both gamma and beta
Tc99m -emits gamma rays only
state the isomeric transition of rubidium-81
Rb81….B+, gamma, 4.7h….>Kr81m…..gamma,13s…>Kr81…..gamma…>stable Br81
what is a positron?
this is a positive beta particle.
what happens in Beta + decay?
radionuclide with neutron deficit may lose energy and become stable by a proton within the nucleus changing into n and e+. The latter is ejected from the nucleus with high energy and is referred as positron/ +ve beta particle.
what happens to mass and charge in B+ decay?
they are conserved.
A= p+n
Z=p=e
Z -1
A the same
what happens in K electron capture?
the nucleus may increase its no of n by capturing an extranuclear e from the nearest k-shell.
p+e = n
The daughter nuclei will emit K characteristic xrays when an e from an outer shell fills the hole created in the k shell.
what would happen when an e from an outer shell fills the hole created in the k shell in K electron capture process?
The daughter nuclei will emit K characteristic xrays when an e from an outer shell fills the hole created in the k shell.
If its left in the excited state , it will produce gamma rays.
Give example of k electron capture:
How much x-rays and gamma rays do they produce?
I123 decays wholly by electron capture and emits:
160 KeV gamma and 28 KeV X rays but NO positive beta particles.
T/F?
Gamma rays have identical properties to x rays
True
re I131, how much gamma rays do they produce?
360 KeV
what does internal conversion mean?
the gamma rays emitted by some nuclei do not leave the atom but are photoelectrically absorbed within its k-shell. as a result they emit both photoelectrons and characteristic x rays, usu of fairly low energy.
why is I123 more useful than I125?
because of its higher energy photon emission and shorter half life- 13h
what is Emax with regards to beta rays?
beta rays are emitted with a continuous spectrum of energies up to a max Emax, which is characteristic of that radionuclide
Their average energy is Emax/3
T/F?
The range of beta particles is proportional to density of the material,
false
It is inversly proportional.
The most energetic beta rays have a range of a few mm in tissue.
what is positron emitters?
when a B+ becomes to its end of range it combines with a nearby e-. The opposite charges cancel each other out and their masses combine and are converted to energy.
the mass of each e = 511 kev. when the two e annihilate each other the energy is emitted as two photons of annihilation radiation travelling in opposite direction
give one example of positron emitters
PET imaging
T/F?
Radioactive disintegration is a stochastic process ie statistical law of chance
true
how do we measure the radioactivity quantity?
by transformation rate, ie the number that disintegrates per second, also known as decay rate.
T/F?
radioactivity is measured by the ‘population’, the mass and number of radioactive atoms.
False
it is measured by decay rate or transformation rate.
what is the SI unit of radioactivity?
Becquerel Bq = 1 disintegration per sec
what is the natural radioactive content of human body?
2 kBq- 2000Bq
what is 1MBq?
1MBq = 1,000,000 Bq
1GBq = 1,000,000,000 Bq
Curie old unit- 1mCi = 37 MBq
what is the relationship between count rate and activity and no or mass of radioactive atoms in the sample.
there is a proportionality:
count rate § activity § no or mass of radioactive atoms in the sample.
define count rate:
This is the number of counts per seconds- cps
what is the exponential law;
the basic law of radioactive decay states that the activity of a a radioactive sample decreases by equal fractions (%) in equal intervals of time.
define half life;
the half life of a radionuclide is the time taken for its activity to decay to half its original value.
eg 10 half lives reduce the activity by a factor of 2*(10)
T/F?
The half life is affected by heat.
False
the half life is unaffected by any agency such as heat, pressure, electricity and chemical reactions.
T/F?
The half life is affected by chemical reactions.
false
T/F?
The radioactivity never falls to 0
True
Exponential decay.
what is a radiopharmaceutical?
this is a pharmaceutical that has been labelled with a radionuclide.
what is the difference bwn biological and physical half life?
If the pharmaceutical is administered alone, it is usually eliminated from thetissues by usual metabolic process of turn over and excretion- biological half life
if the radiopharmaceutical is stored in a bottle, its activity decays with its physical half life.
what is the effective half life?
this is shorter than either biological or physical halflives.
1/teff= 1/tbiol + 1/tphys
what does the effective half life depend on?
it depends on the radiopharmaceutical used and the organ involved and can vary from person to person, depending on their disease state.
T/F?
All nuclides are stable..
False
Hydrogen consists of 1 proton.
what are the desirable properties of a radionuclide for imaging?
- physical half life of few hrs
- decay to a stable daughter or at least one with a very long half life
- emission of gamma rays with no alpha or beta particles nor very low energy photons
- decay by isomeric transition or e capture is preferred
- emission of gamma rays of energy 50-300kev and ideally about 150kev- high enough to exit the patient but low enough to b collimated and easily detected.
- monoenergetic beam so that scatter can be eliminated with PHA
- easily and firmly attached to the pharmaceutical at room temp but has no effect on its metabolism
- readily available
- a high specific activity
what type of decay is preferable in radiox?
decay by isomeric transition or electron capture is preferable
what is the half life of Tc 99?
200,000 years
T/F?
the effective half life should be similar to duration of examination to reduce the dose to patient.
True
list some other properties of radiopharmeceutical;
low toxicity
form a stable product both in vitro and in vivo
be readily available and inexpensive per patient dose
localise largely and quickly in target
how could you reduce the decay during transport and storage for a short lived radionuclide?
if it could be supplied with its longer lived parent in a generator.
re Tc99m
its gamma energy
half life?
supplied from?
Its gamma energy of 140 kev
easily collimated and absorbed in thin crystal
half life of 6 hrs
pure gamma emission- large activity can be administered-reducing noise in the image
how is Tc99 produced?
supplied from a generator shielded with lead. this contains an exchange column of alumina beads on which they have been absorbed a compound of the parent Mo99- which can be produced in a reactor and and has a 67hr half life
what is transient =m?
when the generator is delivered, the activity of daughter Tc99m has built to its max, = to its parent Mo99.
The daughter is decaying as quickly as it is being formed by the decay of its parent. It is said to be in transient equilibrium with the parent.
The daughter and parent decay together with the half life parent 67 hrs
Thereafter the eluant decay with its own half life of 6hrs.
sodium pertechnetate 99m is used for imaging the tissue. Why?
what are the uses?
sodium pertechnetate 99m is used for imaging the tissue base on the account of similarity to iodide and chloride.
It is used in gastric mucosa (localisation of Meckel’s diverticulum), thyroid, and salivary gland.testicular imaging and gastric emptying studies
what do you use for bone imaging?
Methylene diphosphonate- MDP for bone imaging
what do you use HMPAO for?
Hexamethyl propylene amine oxime-HMPAO- for cerebral imaging
what do you use for renal strudies?
dimercaptosuccinic acid- DMSA and MAG3
what do you use for biliary studies?
HIDA- Iminodiacetic acid
what do you use for imaging of liver, spleen and red bonemarrow?
human serum albumin-HSA colloidal particles, 0.5microm in size, these are phagocytosed in reticuloendothelial cells.
lung perfusion imaging, what would you use?
HSA macroaggregates- 15-100 microm microsphere that temp block a small fraction of the capillaries in lung perfusion imaging
Lung ventilation studies
DTPA aerosol
cardiac function?
autologous red cells
spleen?
heat damaged autologous red cells
cardiac perfusion imaging?
sestamibi or tetrofosmin
where is iodine metabolised?
it is metabolised by the thyroid
where is I131 produced?
it is produced in the reactor and has a long shelf life.- 8 days- but emits beta rays as well as rather energetic gamma rays - 364kev. it has been replaced by I123.
where is I123 produced?
its made in cyclotron , more expensive, half life of 13hrs and decays by electron capture, emitting 159 kev gamma rays.
what is half life of I125?
name one use;
60 days-
it has low photon energy 30 kev
mifght be labelled to hippuran for renal studies
I131
I125
name their uses;
for therapy and for thyroid ablation and as brachytherapy seeds.
where is Xe produced?
half life?
how much gamma rays?
uses?
in a reactor
half life of 5.2 days and emits beta rays and rather low energy -81kev gamma rays
inert gas, soluble in blood and fat, when used with rebreathing , in lung ventilation imaging.
re Krypton 81m where is it produced? half life? how much gamma rays? uses?inert gas
generator produced.
half life of 13s
190 kev gamma rays
the generator is eluted with compressed air, the pt inhaling the air Kr81m mixture in pulmonary ventilation studies.
the short half life of parent Rb81, 4.7 h, presents transport difficulties. must be used on the day of delivery.
re Gallium 67 where is it produced? half life? how much gamma rays? uses?
cyclotron produced half life of 78h decays by electron capture 3 main energies: 93, 185, 300 kev Gallium citrate is used to detect tumours and abscess as it binds to plasma proteins.
re Indium111 where is it produced? half life? how much gamma rays? uses?inert gas
it is cyclotron produced half life of 67h decays by electron capture emitting 173, 247 kev gamma rays used to label WBC and platelets for locating abscesses and thromboses respectively.
re In 113m where is it produced? half life? how much gamma rays? uses?inert gas
sometimes used instead of In111
generator produced
half life of 100min
emits only gamma rays but they have a high energy-390 kev
re thallium 201 where is it produced? half life? how much gamma rays? uses?inert gas
cyclotron produced 73h decays by electron capture 80- kev xrays analogus of potassium, used as thallus chloride in myocardialperfusion
what is the most common PET radionuclide?
- F18, half life of 110 min
used in form of 2 FDG for brain and heart metabolism as well as epilepsy and tumour detection. - C11(20min), N13(10min), O15(2min), Rb82(75sec)
Rb82
froduced from strontium 82 generator lasts about 1 month, can be used for myocardialperfusion
Tc94m
where is it produced?
half life?
uses?
cyclotron produced
50 mins
it can be used to label many pharmaceutical already available for Tc99m imaging.
how do you transfer components bwn sterile vials?
shielded syringes to transfer components bwn sterile vials
manipulations are carried under sterile condition in a workstation
room should be under a +ve pressure of filtered sterile air.
the radio-pharmacy must meet the conditions of both the……..and the …….. in the UK
the radio-pharmacy must meet the conditions of both the..medicines Act..and the ..Ionising Radiation Regulation… in the UK
T/F?
using the microprocessor control reduces the radiation exposure of the staff.
True
how do you test for chemical purity?
for example the spot colour test for alumina, which may have come from the Mo99 column and would interfere with labelling.
how do you test forradiochemical purity?
eg testing for free pertechnate in a labelled Tc99m compound using chromatography
how do you test for sterility testing and pyogen testing?
the results are only available restrospectively
for example after the main part of eluant has been used.
T/F?
A gamma ray cannot be focused.
true
since the gamma ray cannot be focused, what would you do to delineate the image from the ptient?
a multi hole collimator is used instead.
why would gamma camera have heavy lead shielding?
to attenuate unwanted background gamma radiation coming from the patient generally, any other sources in the room and building materials.
describe the configurtion of the multi-hole collimator;
it consists of a lead disc-25mm thick, 400mm idiameter. drilled with 20,000 holes each 2.5mm diameter, separated by a 0.3mm thick septa. this absorbs all but few % of rays that are attempting to pass through obliquely.
the HVL of lead for Tc99m gamma rays is…..
0.3mm
T/F?
there is a large number of tiny detectors behind the collimator in planar imaging
False
There is a large single phosphor crystal 500mm in diameter and 9-12 mm thick usually made of NaI- activated with a trace of thallium.
what is the phosphor crystal made of?
usually made of NaI- activated with a trace of thallium.
NaI(TI)
having aahigh atomic number Z= 53 and density it absorbs 90% of Tc gamma raysby the photoelectric process but only some 30% from I131
tell us a bit about NaTI
high atomic number- Z= 53
absorbs 90% of gamma rays by photoelectric process
it is fragle and easi;ly damaged by temp change
how would you protect the crystal from light and moisture from the atmosphere?
It is encapsulated in an Al cylinder with one transparent face.
The transparent face merges the light photons
what could maximise transfer of light from crystal to the photomultiplier tube?
a light guide , a flat transparent plate.
what do you know about photomultipliers?
they consist of an evacuated glass envelope containing a photocathode on the left which is coated with a material that absorbs light and emits photoelectrons. they are accelerated towards the +ve anode. On their way their strike upon dynodes which are connected to progressively increasing positive potential.
when they strike on dynodes they release 3-4 e and they strike the next dynode and etc.
the size or height of the Z pulse is proportional to what?
it is proportional to the gamma ray energy in kev absorbed by the crystal.
what does the PHA make of?
A photopeak
A tail
the pulses produced in the photo peak are produced by the………in the crystal of those gamma ray photons
complete photoelectric absorption.
what does the tail contain?
it contains pulses of lower energy mostly produced by those gamma rays that have suffered Compton interactions in either the patient or the crystal.
what part of the pulse height contributes to locating the position of radioactivity in patient?
the photo peak
PHA is used to reject those in the compton tail.
the pulses that are selected through the PHA are referred to as …….
counts
T/F?
in the case of Ga67 and In 111 two or three windows must be used simultaneously, each selecting one of the emitted gamma ray energies.
True
how would you send the x, y and z pulses to the computer?
via analogue to digital converters.
this enables dynamic and gated studies to be undertaken as well as a range of image processing.
the computer records each…….pulse as a count in the memory location that corresponds to x and y coordinates
Z pulse
what does the brightness of the image depend on?
It depends on number of counts stored in the corresponding memory location.
what sort of post processing could be done?
contrast enhancement by windowing
noise reducing by averaging
matrix increased by pixel interpolation
image subtraction can also be done.
What do we use mobile gamma camera for?
For cardiac imaging
used in cardiac lab and ITU
what are the dimensions of cardiac camera (ie mobile)
250mm field and a crystal 5 mm thick- give good spatial resolution with 80 kev gamma rays from TI201.
a large FOV 500mm can take in whole wifth of pt. where would you use that in?
in bone and gallium imaging.
a scanning gamma camera in which the camera head transverses along the long axis of supine pt, effectively increases the image matrix.
T/F?
the more holes there are, the wider they are, or the shorter they are, the greater the sensitivity.
true
less radionuclide needs to be administered and so less patient dose
name different types of collimator; state their uses
parallel- FOV, in air sensitivity is the same.
divergent- smaller diameter, larger FOV, minifies the image, eg lung, geometrical distortion
convergent- magnifies the image, smaller FOV, used in children and small organs,geometrical distortion
pin hole- magnified but inverted image of a superficial small organ, eg thyroid
which collimators magnifies the image?
convergent
which collimators magnifies and inverts, used in thyroid?
pin hole
which collimators minifies the image with large FOV?
divergent
where is resolution best?
resolution is best close to the collimator.
T/F?
The wider the collimators are, the shorter they are, more gamma rays are seen, so greater sensitivity , but the worse the SR
True
better the resolution the less the sensitivity.
T/F?
It is not possible to max both sensitivity and SR
True
something has to be compromised eg FOV
list different types of collimator;
- Low energy- thin septa- 0.3mm
- Medium energy- 400 kev, 1.4 mm septa, fewer holes, less sensitivity
- General purpose- 2.5mm, 20,000 holes , 150 cps
- High resolution- more and smaller holes, lower sensitivity
- High sensitivity- fewer and larger holes, poor resolution, dynamic imaging, short exposure.
How could you define region of interest?
By a cursor and the total counts therein measured on each frame and displayed as a function of time.
where would you start the sequence when performing the cardiac studoes?
each sequence is initiated by the R wave form from ECG.
how could you reduce the imaging time or improve the sensitivity ?
By using a dual or triple headed camera/
T/F?
Fewer counts from the centre than from the edges.
true
How could you correct the attenuation?
you could add counts, pixel by pixel, in each pair of opposing views
go through the single photon emission computed tomographyon page 132s
..
what is the disadvantage/limitation of using filtered back projection in nuclear medicine?
the area with high activity eg bladder or inj site can cause streaking of the image and even hide adjacent areas of activity.
what is the alternative algorithm to filtered back projection?
iterative reconstruction.
what is the most common positron emitters in PET?
F18
what is the basis of PET imaging?
is to detect the two annihilated photons in coincidence and to identify their origin in the patient to locate the radioactive source.
what is a PET camera/ positron composed of?
It comprises a ring, hexagon or other polygon surrounding the patient. it composed of a very large no of solid scintillation detectors (10,000-20,000).
what is the scintillation detectors made of?
bismuth germiate- BGO
or lutetium oxyorthosilicate- LSO
or gadolinium oxyorthosilicate-GSO
what are the criteria for ideal detectors?(3)
readily available cheap to produce easy to manufacture into crystal blocks. it should have - high detection efficiency - very short decay time good energy resolution
T/F?
the detectors are made in block format and they are coupled to photomultiplier tube.
true
what are the three types of coincidence that can occur:
True
Random- from independent events, may not occur in the same plane
Scatter
what is the axial FOV?
it is the width of the complete set of rings
T/F
Each slice has its own sinogram.
true
Define line of responce-LOR;
this is the sum of activity along a line
How could you reduce the random and scatter coincidence?
by using narrow lead and tungsten septa and parallel anti-scatter grid
what does the attenuation depend on in PET scan?
it depends on patients dimensions and tissue structure
What sort of correction would you use for larger organs where the LOR are away from the centre?
arc correction.
list the data acquisition in PET;
2D- using septa and producing sinogram
3D- higher scatter fraction but higher sensitivity, producing a sinogram called Michelogram
T/F
The effective dose is higher in PET than gamma imaging.
false
the effective dose is the same as gamma imaging.
compare the SR of PET and SPECT
SR of SPECT is poor compared to purpose built PET
T/F
The dual headed conventional gamma cameras used for planar imaging or SPECT can be used to function as PET scanners.
true
data are obtained by rotating the camera around the patient without the collimator in place.
t/f
the sensitivity for NaI crystals is much higher than for BGO
false
its much lower so a thicker crystal will give better results and the higher background noise reduces contrast in the image.
define source organ and target organ
source organ is the organ of interest
target organ- irradiation as a result of source organ radiation.
the absorbed dose increases in proportion to what?
- activity administered to patient
- fraction taken up by the organ
- effective half life of activity in organ
- energy of ß/¥ radiation emitted
t/f
very little of ß ray is deposited inside the organ
false
almost all ß ray is deposited inside the organ, very little escapes.
what does the uptake depend on?
body weight and size disease age/sex diet drugs.
t/f
the dose is affected by the no of images taken
false
the dose delivered is unaffected by no of images taken.
what is the effective dose in
nuclear medicine
bone/static brain
NM
who sets the limitation for the activity administered?
it is set by the country- in UK this would be ARSAC
how would you check the accuracy of the callibrator?
by using a long lived source- Co57
the callibrator can also be used to check the purity of radionuclide
t/f
the inverse square law also applies to the NM
true
t/f
lead aprons can provide adequate protection against ¥ rays.
false
they are ineffective against high energy gamma rays.
What sort of calculations are used to measure the internal absorbed dose?
Monte Carlo
